“Battle of the sexes” is an expression commonly used as a title for fatuous dating shows and cheap boardgames. As of late, however, geneticists have been debating the battle of the sexes at the level of chromosomes. The infamous Y chromosome is an assemble of genes that, when paired with an X chromosome, produces a male off-spring. Yet the genes that comprise the Y chromosome have been in stark decline in the last few hundred million years, making biologists question whether the Y chromosome is at the edge of extinction. Unfortunately for women who fantasize about a world devoid of men, a recent study suggests the genes that comprise chromosomes in men are not going extinct.
The suggestion that the Y chromosome is gradually dissolving with time gained significant traction by scientists in recent years for a variety of reasons. The X and Y chromosomes used to have so much in common, sharing approximately 800 genes. As with most relationships that age, the biological attraction that once bonded the chromosomes has has dwindled with time, currently sharing only 17 common genes.
Yet the genetic rift between the chromosomes has not just changed in number, but size as well. The X chromosome holds approximately 1,089 genes. The Y chromosome holds only 78 genes and has lost 90 percent of its genetic material. Furthermore, the suggestion that a species can gradually lose a chromosome over time is not just abstract theorizing, but can readily be found in nature. For example, a species of rat located off the coast of Japan known as Ryukyu have completely lost their Y chromosome; although, the rats are still capable of producing male off-spring, since the genetic material once stored in the Y chromosome is now stored in X chromosome. As Ian Malcom infamously stated in Jurassic Park, “Life will find a way.”
In fact, humanity has already lost an essential chromosome in its own time. It is one of the many ways biologists have confirmed we share a common ancestor with the great apes, gorillas, chimpanzees and orangutangs. The great apes have 24 chromosome pairs; humans have only 23 chromosome pairs. Evolutionary theory predicts that if we share a common ancestor with the great apes, then one of those chromosome pairs must have been fused together, whose relics can be found in our genetic constitution. When scientists scanned the human genome, they found that our chromosome number two is actually the product of two chromosomes that fused together in the distant past. It’s there, testable and confirms the prediction made by evolutionary theory.
Contrary to popular reasoning, a recent study published in journal PLOS Genetics suggests that the chromosomes found in men are not going extinct. As was already known but less widely reported, the rate of gene loss in the Y chromosome has drastically halted. What the researchers found is that natural selection has chiseled the Y chromosome down do the genes that are essential to human functioning. Rather than gradually dissolving, the Y chromosome is gradually being sharpened by natural selection.
The Y chromosome is cast in the shadow of the X chromosome. In women, however, X chromosomes come in pairs and are able to exchange information in an effort to fix whatever genetic defects that might occur. In contrast, the Y chromosome in men is incapable of swapping genetic information with the X chromosome. Due to this, natural selection has gradually chiseled the Y chromosome down to its foundation in an effort to weed out superfluous genes that carry the risk for acquiring genetic mutations. Since the chromosomes in men are not going away anytime soon, it appears the battle of the sexes remains an evolutionary arms race without end.
By Nathan Cranford